The present invention consists in apparatus for transporting and installing a deck of an offshore oil production platform.
Offshore oil production platforms generally include a deck carrying production equipment and crew's quarters.
The deck is supported by tubular piles or legs driven into the sea floor or resting thereon on shoes.
There are various ways to install this kind of platform at the production site.
The first consists in floating all of the platform to the production site, lowering the legs until they contact the sea floor and then, using the legs as supports, raising the deck above the water to a height such that it is out of reach of the highest waves.
The second installation method consists in first placing the legs on the sea floor and transporting the deck of the platform from the assembly yard to the site on a barge with dimensions compatible with the size of the deck.
The problem is then to transfer the deck from the barge to the upper ends of the legs, because the deck is on a floating body affected by swells and, like the body carrying it, is subject to a continuous orbital motion the amplitude of which depends on the height of the swell.
What is more, the deck has a very high mass, possibly several thousand ton, which does not facilitate transferring the deck.
The barge carrying the deck is placed between the legs of the platform and the deck is transferred from the barge to the legs of the platform either by ballasting the barge or by lifting equipment on the barge.
Ballasting the barge is a lengthy operation which takes several hours and the height to which the deck is raised is small, which means that this method cannot be used to install the deck at places where heavy seas may be experienced because it will not be at a sufficient height to be out of reach of the highest waves.
Raising the deck by means of jacks has the main drawback that jacks are sensitive to lateral forces, making it necessary to install protection and guide structures that add to the weight of the equipment installed on the barge.
Moreover, the travel of jacks is limited.